Socioeconomic status and heterogeneity in aging As people get older there is increasing heterogeneity in health and in physical, mental and cognitive functioning, resulting in age peers becoming more and more dissimilar from each other. Research on the determinants of this heterogeneity is crucial as positive health trajectories are related to higher quality of life, longer independence and considerably lower medical and social care costs. The Whitehall II study on 10,308 British civil servants was set up in 1985 and has played a crucial role in shaping the research agenda on social inequalities in health. Over the last 22 years participants, now aged 55-79 years, have been followed up with medical examinations at 5-year intervals and with questionnaire surveys every second or third year. Thus, Whitehall II is now primed to address one of the major challenges of the new millennium; determinants of heterogeneity in health in ageing populations. NIA support has been crucial to the addition and exploitation of functioning data in the Whitehall II study. As the participants age, this application seeks continued NIA support for further analysis of the data collected so far and to collect two more phases of data over the next 5 years. This support will enable us to address three overall aims. 1) Social inequalities in chronic diseases, mortality and functioning: To examine whether relative and absolute social inequalities in chronic diseases (coronary heart disease, stroke, diabetes) and mortality increase with age and to estimate the importance of biological, behavioral and psychosocial explanations of these inequalities. To examine the contribution of repeated measures of risk factors to contemporaneous, trajectory and accumulated risk models. To determine whether the consequences of disease on functioning differs or are moderated by socioeconomic status. 2) Cognitive changes in early old age: determinants and consequences: To examine the socioeconomic, vascular and behavioral determinants of heterogeneity in cognitive aging, starting in midlife, and to assess the consequences of cognitive decline on physical, social and mental functioning and mortality. 3) Social participation: impact on health and functioning in early old age: To examine the socioeconomic and gender patterning of social participation trajectories over the adult life course. To examine the effects of social participation on functioning and chronic disease and to address the issues of reverse causation and confounding in the association between social participation and health. The relevance of our research is tied in with continuing increase in life expectancy and the need to identify potentially modifiable risk factors to improve overall health and reduce social inequalities in the health of older populations. Aging trajectories appear to diverge fairly early on and our data on a multitude of risk factors and health measures on individuals from early mid-life to old age are an important resource to study the determinants of heterogeneity in aging trajectories.